Electroluminescent device having a field-effect transistor addressing system



3,246,l 62 -EF'FECT Aprl 12, 1966 TE NING CHIN ELECTROLUMINESCENT DEVICEHAVING A FIELD TRANSISTOR ADDRESSING SYSTEM Filed March 24, 1965 5Sheets-Sheet 1 INVENTOR. 7.? /V/vc: C/ /A xt x.

arra/amy April 1966 TE NING CHIN 3,246,162

ELECTROLUMINESCENT DEVICE HAVING A FIELD-EFFECT TRANSISTOR ADDRESSINGSYSTEM Filed March 24, 1965 3 Sheets-Sheet 2 gp L INV EN TOR.

April 12, 1966 Filed March 24, 1965 TE NING CHIN 3,246,162ELECTROLUMINESCENT DEVICE HAVING A FIELD-EFFECT TRANSISTOR ADDRESSINGSYSTEM 5 Sheets-Sheet 3 INVENTOR. 7? /V//v' C//m/ United States Patent OELECTROLUMINESCENT DEVICE HAVING A FIELD-EFFECT TRANSISTOR ADDRESSINGSYSTEM Te Ning Clin, Princeton, NJ., assignor to Radio Corporation ofAmerica, a corporation of Delaware Filed Mar. 24, 1965, Ser. Ne. 445,8397 Claims. (Cl. 250-211) This invention relates to electroluminescentdisplay devices. In particular, this invention relates to an improvedelectroluminescent device, including a novel addressing means orsystems.

This application is a continuation of my copending application SerialNo. 62,594, filed October 14, 1960, now abandoned, assigned to the sameassignee.

In the prior art, there are many known types of electroluminescentdevices. In general, an electroluminescent device comprises anelectroluminescent phosphor positioned between two ele ctricallyconductive electrodes. When a potential of appropriate magnitude andfrequency is applied between the electrodes, the electroluminescentphosphor is excited and produces light. In order to make a visibledisplay of information from an electroluminescent lamp, or panel, somemeans must be utilized to electrically energize only certain selectedareas of the electroluminescent phosphor so that the light emission isin the configuration of an image, a letter, a number or other desiredshape.

In the prior art there are several known means for addressing orenergizing the electroluminescent phosphor in the desired manner.Examples of these addressing means include photoconductive elements,ferro-electric elements and inductive .type devices. The inductive typeand ferro-electric type devices have been used in electrically addressedsystems while the photoconductive type device has mainly been used inoptically addressed systems.

It has been found that these prior systems or devices have certainlimitations. Amongst these limitations is the problem of manufacturingan electroluminescent device including a sufficently large number ofaddressing elements within a predetermined area so that theelectroluminescent image will have proper picture definition. Another ofthe limitations on these prior devices is that, generally, theaddressing systems can be energized either by electrical input or byoptical input but not by both.

It is therefore an object of this invention to provide an improvedelectroluminescent device.

It is a further object of this invention to provide an improvedelectroluminescent display device having an addressing system which canbe either optically or electrically energized and which is characterizedin its relatively small Volume for each elemental unit.

These and other obje-cts are accomplished in accordance with thisinvention by providing an electroluminescent device each elemental unitof which includes an electroluminescent cell and a unipolar transistor.The unipolar transistor may be energized by either light or electricalsignals. By energizing selected ones of the unipolar transistors,selected electroluminescent -cells are turned on. By properly selectingthe unipolar transistors to be energized, scanning lines or a completeimage may be made to enit light.

The invention will be more clearly understood from the followingspecificaton when read in connection with the accompanying three sheetsof drawings, wherein:

FIG. 1 is a partially schematic view of an elemental unit of anelectroluminescent panel made in accordance with this invention;

FIG. 2 is a partially schematic sectional View of an ice otherembodiment of this invention;

FIG. 4 is an enlarged fragmentary sectional View of a further embodimentof an electroluminescent panel in ac cordance with this invention; y

FIG. 5 is an enlarged fragmentary sectional view of still anotherembodiment of this invention;

FIG. 6 is a schematic circuit diaphragm of an embodiment of theinvention in which electrical switching is employed.

FIG. 7 is an enlarged fragmentary sectional View of anelectroluminescent panel and associated cells incorporating theinvention shown schematically in FIG. 6; and

FIG. 8 is a plan view of the panel shown in FIG. 7.

Referring now to FIG. l, there is shown a series circuit including anelectroluminescent cell 10 and a unipolar transistor 12. Theelectroluminescent cell 10 comprises two spaced electrodes 14 and 16,having an elec tr oluminescent phosphor 18 positioned therebetween. Theelectrodes 14 and 16 may take any desired shape, e.g. the cells may bein the shape of number or letter. At least one of the electrodes 14 or16 is transparent. An example of materials which have been used aselectrodes of electroluminescent cells is a transparent de- -posit oftin-oxide that is positioned on a transparent support plate (not shownin FIG. 1). The electroluminescent phosphor 18 may comprise any knownelectroluminescent phosphor material mixed with a suitable bindingmaterial. One example of an electroluminescent phosphor material is Zincsulfide while an example of a suitable binding material is a plasticsuch as an epoxy resin.

Connected electrically in series with the electroluminescent cell 10 andthe unipolar transistor 12 is an alternating current, or pulsed directcurrent power supply 20. The unipolar transistor 12 comprises a layer ofsemicondu cting material, such as silicon, having P and N regionssimilar to those shown and having a 'diffused junction illustrated bydotted line 22. Unpolar transistors are 'described in an article by W.Shockley, entitled, "A Unpolar Field-Etfect' Transistor," appearing inthe Proc. IRE vol. 40, :pp. 1365-1376 (1952). Generally, in a unipolartransistor, the conductivity of the layer of semi-conducting materialfrom the source to the drain is modulated by a transverse electric fieldsupplied by means of signal input or gate ele ctrode 24. The unipolartransistor 12 is a relatively high resistance device, for example 20,000ohms, when no gate signal is applied to the input or gating electrode24, while it is a relatively low resistance device, for example 2,000ohms, when a gate signal is applied to the input electrode 24. Since theamplifying action of the transistor involves currents carriedpredominantly by one kind of carrier, this device is known as a unipolartransistor. The change in conductance between the two N-type regions,i.e. the source to the drain, results from changing the number ofcarriers of this one type.

The elemental unit shown in FIG. 1 comprises a series connectedarrangement of the electroluminescent -cell 10, the unipolar transistor12 and the power supply 20. When no gate signal is applied to the inputor sig nal gate wire 24, the resistance of the transistor 12 is high ascompared to that of the electroluminescent cell 10 so that substantiallyall of the volt-age drop of the voltage from the power source 20 occursin the unipolar transistor 12. Since most of the voltage drop occursacross the unipolar transistor 12, no light is produced by theelectroluminescent cell 10.

When a positive (for this unipolar transistor) signal voltage is appliedto the input terminal 24, the resistance &246462 of the unipolartransistor 12 is decreased substantially so that a 'large portion of thevoltage drop of the voltage from the power source 20 now occurs acrossthe electroluminescent cell 10. When the signal is applied, the

'phosphor is energized and light is produced or emitted by the phosphor10. v

The resistance of the unipolar transistor 12 may be varied by applying asignal voltage to the electrode 24 or, in the alternative, a constantpotential may be applied to the electrode 24 and a light directed ontothe unipolar transistor 12. The resistance of the unipolar transistor 12will decrease in response to light somewhat similar to the well-knownphotoconductive action. Thus, in the elemental unit shown in FIG. 1,when a signal pulse is applied to the electrode 24, theelectroluminescent element will produce light. If the light from theelectroluminescent element 10 lands on, or is fed back to, the unipolartransistor 12, the unipolar transistor 12 will remain in its lowresistance condition after the signal pulse is removed and will thus,keep the electroluminescent cell energized. Thus, with light feedbackbetween' the electrolurninescent cell 10 and the unipolar transistor 12,storage of the input information may be obtained.

Referrng now to FIG. 2, there is shown a fragmentary section View of asingle line of a light scanning device made in accordance with thisinvention. The device -comprises a transparent :support member 26 whichmay be made of a material such as glass. Since light is fed through thesupport member 26, the support member should be relatively thin, e.g.inch, in order to prevent loss of picture resolution. On one surface ofthe support member 26 there is provided a continuous electricalconductor 23. The conductor 28 is transparent to the wave-lengths oflight which are emitted by the electroluminescent cells. Theelectroluminescent cells comprise a plurality of electroluminescentphosphor dots or areas 30 each covered by a different one of a pluralityi of conductors 32.

On the opposite surface of the transparent support plate 26 is provideda plurality of unipolar transistors 34. Each of the unipolar transistors34 is in light receiving relationship with respect to a different one ofthe electrolumnescent 'phosphor areas 30. The conductor 32 iselectrcally connected to the drain side of the unipolar transistor 34that is positioned adjacent to, i.e. not in light feedback relationwith, the particular electroluminescent cell. The source sides of all ofthe unipolar transistors 34 are connected to a common pulsating sourceof potential 36. The other side of the source 36 is connected to thetransparent conductor 28.

During operation of the light scanning line shown in FIG. 2, when thefirst electroluminescent cell 30a is energized, light from this cellwill fall on and decrease the resistance of the first unipolartransistor 3411. On the next pulse from the source 36, theelectrolurninescent cell 30b will be energized, which will "make readythe unipolar transistor 34b in that unit. Thus, each time a pulse isapplied from the source 36, the spot of light will move down oneelemental unit. Ea-ch of the elemental units in back of the elementalunit now emitting light will be continuously energized. It should beunderstood that a large plurality of lines of the type illustrated bythe single line shown in FIG. 2, may be applied to one transparentsupport member and a complete moving spot panel device provided. Themoving light spot may be stopped at any desired position, to indicateany particular information, by stopping the pulses from the source 36.Also, the moving spot may be started at any position along a line byshining a light on the selected unipolar transistor in any selectedline. The direction of the light spot movement will always be from leftto right, as illustrated in the drawings, since this is the onlydirection of light feedback.

The panel shown in FIG. 2 may be manufactured, for example, by sprayingtin oxide, as the conductors 28,

onto the support member 26 through a suitable mask. Theelectroluminescent phosphor areas 30 may also be deposited by sprayingthrough a suitable mask. The array of unipolar transistor 34 may be madeby the integrated circuit techniques through the known diffusion andlapping processes. The connections to the unipolar transistors, andbetween the unipolar transistor 34 and the electrolurninescent cells maybe made by printed circuit techniques. Using these techniques,"elemental units of approximately 0.08 inch square have been made whichproduce a light output of approximately 0.13 lumen per square. Theseelemental .electroluminescent cells can be controlled by unipolartransistors, for example, of properly doped silicon having a ohm-cm.channel width of approximately 0.0016 cm. and a channel length ofapproximately 0.054 cm.

Referring now to FIG. 3, there is shown an em bodiment of this inventionwherein a relatively thick support member 38 may be utilized. Thesupport member 38 may be made of any transparent material, such asglass, and has a continuous line of transparent, electrically conductivecoating '40 on one surface thereof. On the transparent conductivecoating 40 thre is provided a plurality of spaced apartelectroluminescent phosphor areas `or dots 42. Each of the phosphorareas 42 is covered by a different transparent electrically conductivecoating 44. On each transparent conductive coating 44 there is provideda different light transparent layer of electrical insulator 4'6 whichmay be a material such as plastic. `On each of the electrical insulators`46, there is provided a different unipolar transistor 48. A pulsatingsource of potenital '50 is connected between the transparent coating 40and source side of each of the unipolar transistors 48. The drain sideof each unipolar transistor 48 is connected to the next .adjaoenttransparent conductor 44, i.e. to the conductor 44 of an adjacentelectroluminescent cell. Thus, When a unipolar .transistor 48 is in itslow resistance state, the electroluminesoent c-ell to i ts right, asshown in the drawings, produces light which decreases the -resstance ofits respective unipolar transistor 48.

T-he operation of the embodiment shown in FIG. 3 is substantially thesame as that of the em bodiment shown in FIG. 2. Also, a plurality ofdifferent coatings 40 can be provided on the same support member,arranged in rows, and a two dimensional display provided.

Referring now to FIG. 4, there is shown an embodiment of this inventionwherein the unipolar transistors and the electroluminuescent cells arein a stacked array. The device shown in FIG. 4 comprises a supportmember 52 which is made of a transparent conducting glass having arelatively high resistivity, for example, 1,000 ohmcm. The transparentconducting glass may :be any of the known transparent high resistancematerials such as Corning x 857AJ commercially available from theCorning Glass Co. On one surface of the ,transparent conducting glass 52is a transparent electrical conductor 54. The transparent electricalconductor 54 may `be made of a material such as tin oxide. The othersurface of the support member 52 includes a plurality of grooves 56extending in opposite direction to form a plurality of spaced apartlands or hills. On each of .the lands bet-ween the grooves `56 isdeposited the gating side of a different unipolar transistor 58. On thedrain side of each of the unipolar transistors '58 there is positioned adifferent electrically conducting plug 60. On each of the conductingplugs '60 there is provided a different electroluminescent 'cell 64.Each electroluminescent cell 64 comprises a transparent conductor 66, anelectroluminescent phosphor 68 and a common conductor 70. On the sourceside of each unipolar transistor 58 there is provided a differentelectrical conductor 72. The electrical conductors 72 are all connectedto a common conductor 74 which extends in a direction at right angleswith respect to the conductors 70.

A source of potential is connected between the conductors 74 and theconductors 70 on each electroluminescent cell. By applying a potentialto the unipolar transistor gate lead 54, selected unipolar transistors 58 in any line may be switched to their low resistance state 'by means ofa light spot on the selected unipolar transistor. This low resistancestate permits the respective electroluminescent cell 64 to be energizedand produce light. When an electroluminescent cell 64 is energized, the.light therefrom will strike its respective unipolar transistor 58 which'will store this 'bit of information. Thus, in the embodiment sho wn inFIG. 4, the electroluminescent panel will. permit a display ofinformation in two dimensions. This display may be Originally energizedby optical means -such as a cathode ray tube or a flying spot lightsource. It should `be understood that the input lighf' may be ofwavelengths other than the Visible spectrum such as infrared, X-ray orultra violet.

It should be understood that the structure shown in FIG. 4 may beconstructed -in various .forms. Thus, a 'line of electroluminescentcells 64 and the conductors 70 may be provided on a support of aperturedglass, e.g. Fotoform, with conducting plugs 60 and 72 in the glass.Also, a second support (not shown) may be provided with theelectroluminescent cells on this support and this structure positionedon top of the conductors 60.

Referring now to FIG. 5, there is shown an embodiment of this inventionwhich may be utilized to produce an image of a scene. In thisembodiment, an electroluminescent cell 76 is connected between aconductor 78, that extends in one direction, and a unipolar transistor80. The other side of the unipolar transistor '80 is connected to aconductor 82 that extends in the transverse direction. Thus, theconductors 78 .and 82 extend at right angles with 'respect to eachother. Any desired electroluminescent element 76 may be turned on byselecting the proper conductors 78 and 82, and -by energizing therespective unipolar transistor in the selected spot. The resistance ofselected unipolar transistors may be de'creased by means of a movinglight spot. Once the unipolar transistor 80 is energized, the decreasein resistance is subtantial and the electroluminescent element 76 in'that unit is turned on. As long as the current is applied to theselected conductors 78 and 82 the selected electroluminescent cell orcells 76 will remain on because of light feedback to the unipolartransistor 80 in each unit. Also, only the selected cell produces lightbecause of the high resistance of the non-energized unipolar transistor.

Re-ferring now to FIG. 6, there is shown an equivalent circuit diaphragmof an embodiment of this invention which is energized electrically. Onlyone line is illustrated in FIG. 6, although a plurality of lines may beused as shown in FIG. 8, extending 'in a two-dimensional array. In thisembodiment, a pair of resistors 84 and 86 are connected electrically inparallel with an electroluminescent cell 88. The parallel combination isconnected to the drain side of a unipolar transistor 90. The source sideof the unipolar transistor 90 is connected to a potential source 92which is of sufiicient magnitude to turn on the electroluminescent cell88 when the unipolar transistor 90 is in its low impedance condition.The unipolar transistor 90 is switched to its low impedance condition bymeans of voltage pulses from the voltage generator 94.

connected between resistors 84 and 86 is a gating lead 96 which `is alsoconnected to the gate electrode of the next adjacent unipolar transistor90. Thus, the first unipolar transistor 90 is turned on by a pulse fromthe source 94 which permits the first electroluminescent cell 88 toproduce light. Part of the light from the electroluminescent cell 88feeds back to the first unipolar transistor 90 and maintains the lowimpedance condition of the latter, as in the elemental unit shown inFIG. 1. The next pulse from source 94 will be fed through the parallelcombination of the electroluminescent cell 88 and the resistors 84 and86 to the gating lead 96 which will provide the low impedance conditionto the next unipolar transistor 90. Thus, this action will switch on thenext electroluminescent cell 88. The resistors 84 and 86 form a voltagedivider which applies only a fraction of the voltage of the pulse source94 to the next unipolar transistor 90.

Thus, in the scanning line shown in FIG. 6, any num- 'cer ofelectroluminescent cells 88 may be turned on by continually pulsing thesource 94. In this embodiment the information applied to the source 94may be any desired information such as the output from a computer orother similar information. With a large plurality of such scanninglines, a two-dimensional display of.information is provided.

Referring now to FIGS. 7 and 8, there is shown a twodimensional panelmade in accordance with this invention and utilizing the circuitillustrated in FIG. 6. The device comprises a transparent support 98having transparent conductive lines 100 deposited thereon. Theconducting lines 100 are, during operation, connected to ground. On thetransparent conducting lines 100 is a plurality of spaced apart'electroluminescent phosphor areas 102. On the exposed side of eachelectroluminescent phosphor area 102 is a different electrical conductor104. One side of each conductor 104 is electrically connected to, andbutts against the `drain end of a different unipolar transistor 106. Theunipolar transistors 106 are supported 'on another glass support plate99. The other side of the electroluminescent cell is an electricalcontact with a resistance film 108, for example, nonactivated zincsulfide. Substantially centrally located on each of the resistance films108 is a different conductor 110, -for example, of silver paste. Each ofthe conduct ors 110 extends from one of the resistance films 108 to thegating electrode of the next adjacent unipolar transistor 106. The otherend of each of the resistance films 108 is connected back to a groundlead 109.

connected to the other source side of each of the unipolar transistors106 is a conductor 113 which is connected to source 114. Connected tothe first unipolar transistor 106 in each row is a pulsating source 116.Thus, the embodiment shown in FIGS. 7 and 8 is a panel device havingcircuits which are the equivalent of that shown in FIG. 6.

When the pulsating source 116 is triggered, the first column of unipolartransistors 106 are actuated or switched to their low resistance statewhich permits the first column of electroluminescent cells 102 toproduce light. The second pulse from the source 114 will automaticallybe applied to the second column of unipolar transistors 106 which willswitch on the second column of electroluminescent cells 102. Then thefirst two columns emit light, etc.

All of the embodiments of this invention may be constructed by knownevaporating, dfiusion and lapping techniques as was explained inconnection with FIG. 2.

In any of the embodiments of this invention, the electroluminescentcells may he elemental units of a composite panel. Also, in any of theembodiments of this invention, the electroluminescent cell or its areamay be in the configuration of a number, letter, or other similarinformation for recording the output of computers and similarinformation reproduction.

What is claimed is:

1. An electroluminescent device comprising: a series of elemental units,each unit comprising an electroluminescent cell, a field effecttransistor and an electrical conductor connecting one side of said cellwith the drain side of said transistor; a source of power, the sourcesides of all of said transistors being electrically connected to oneside of said power source, the other sides of all of saidelectroluminescent cells being electrically connected to the other sideof said power source; means electrically connecting said conductor ofeach elemental unit with the gating electrode of the transistor in thenext adjacent 7 unit; and means' for applying a trigger pulse Voltaget-o the gating electrode of the transistor in the first unit of saidseries.

2. An electrolurninescent device as in claim 1, wherein said transistorshave photoconductive properties and each transistor is exposed to lightfrom the electroluminescent cell in the same unit.

3. An electroluminescent device as in claim 2, further including aresistance element connected between said other Side of eachelectroluminescent cell except the last one and the gating electrode ofthe transistor in the next unit of said series.

4. An electroluminescent device as in claim 3, wherein said connectingmeans includes a second' resistance ele ment.

5. A light conversion device comprising a sheet of light transparentelectrically conducting glass having a relatively high electricalresistance, an electrically conductive coating h'aving a relatively lowelectrical resist- -ance on one surface of said glass, a plurality ofrows and columns of grooves forming a plurality of spaced ap art hillsin the opposite surface of said' glass, a plurality of unipolartransistors, the gating side of each of said unipolar transistors beingpositioned on one of said hills, a first plurality of electricalconductors each connected to the source side of all of the unipolartransistors in a column,-a second plurality of electricalconductors-each on a drain side of a different one of said unipolartransistors, a plu'rality' of el-ectrolurninescent cells each on adifferent one of said second plurality of conductors, and all of saidelectroluminescent cellsin a row being electric'ally connected together.

6. An electroluminescent device comprsng a plurality of units, each unitcomprising an electroluminescent cell and an electrical resistanceelement in an electrically parallel combination, each unit further compris-ing a un'ipolar transistor, the darin side of the unipolartransistor in 'one unit being electrically connected in series` with'said parallel combination in that unit, and an elect-'ical corinectionbetween said parallel combination of one unit and the gating side of theunipolar transistor in an adjacent unit.

7. An electroluminescent device comprising a' plurality of elementalunits, each elemental unit including' a parallel combination of an`electr-olumine'scent cell andi a resistance means, each elemental unitfurther including a unipolar transistor, said units being arranged inrows and columns, a first source of power, the' source side of all ofthe unipolar transistors in a row being electrically connected to saidfirst source of power, the drain side' of said unipolar transistorsbeing electrically connectedto the parallel combination in that unit, asecond source of power connected to the gatin'g side of the first'unipolar transistor in each row, and an electrcal connection hctweensaid resis'tance means in one unit and the gating side of said unipolartransistors in an adjacentunit' in arow.

References Cited by the Examiner UNITED STATES PATENTS 2,985,805 3/1958Nelson 250--211 FOREIGN PATENTS 860,685 2/ 1961 Great Britain. 5773515/1958 Italy.

RALPH G. NILSON, Primary Exam'ne r.

J. D. WALL, Assistant Exam'r'er,

1. AN ELECTROLUMINESCENT DEVICE COMPRISING: A SERIES OF ELEMENTAL UNITS,EACH UNIT COMPRISING AN ELECTROLUMINESCENT CELL, A FIELD EFFECTTRANSISTOR AND AN ELECTRICAL CONDUCT CONNECTING ONE SIDE OF SAID CELLWITH THE DRAIN SIDE OF SAID TRANSISTOR; A SOURCE OF POWER, THE SOURCESIDES OF ALL OF SAID TRANSISTORS BEING ELECTRICALLY CONNECTED TO ONESIDE OF SAID POWER SOURCE, THE OTHER SIDES OF ALL OF SAIDELECTROLUMINESCENT CELLS BEING ELECTRICALLY CONNECTED TO THE OTHER SIDEOF SAID POWER SOURCE; MEANS ELECTRICALLY CONNECTING SAID CONDUCTOR OFEACH ELEMENTAL UNIT WITH THE GATING ELECTRODE OF THE TRANSISTOR IN THENEXT ADJACENT UNIT; AND MEANS FOR APPLYING A TRIGGER PULSE VOLTAGE TOTHE GATING ELECTRODE OF THE TRANSISTOR IN THE FIRST UNIT OF SAID SERIES.